The present invention relates to the liquid-packaging industry, more particularly where the issue is one of designing and manufacturing containers with built-in stopper/dispensers used for packaging liquids that are to be dispensed drop by drop.
Devices of this kind have many fields of application, not only in the world of pharmaceutical or cosmetic products but also, for example, in the case of lubricants or solutions used in the agri-foodstuff industry. The main aim in using them is to keep liquid products which are used only gradually in small amounts for as long as possible, by expelling just a few drops each time.
Very often, the product kept in the flask has also to be protected from any contamination. This is the case, for example, with ophthalmic solutions, that have to be kept away from the ambient air and the bacteria it contains. In practice, the preserving of such solutions follows two routes, which may, incidentally, be used simultaneously. One of these consists in placing an anti-bacterial filter over the conduit through which the drops are expelled, and the other consists in incorporating a preservative into the liquid which has then to be held back so as to rid the expelled product of it.
In the prior art to the present invention, there are known devices for packaging liquids that are to be dispensed drop by drop which comprise a flask, the interior volume of which can be varied by manually deforming its walls, and a dispensing nozzle containing a purifying element inserted in the path taken by the liquid as it is expelled from the flask under the effect of the pressure exerted by reducing the volume of the latter.
Such packaging devices are described, for example, in French Patent 2,638,428 in the name of the applicant. It may be seen in that patent that, in the dispensing nozzle, the conduit for expelling the liquid is preceded by a lock chamber bounded by a purification element upstream, this being capable of holding back the preservative in an ophthalmic solution that constitutes the liquid that is to be dispensed, and by a filtration element downstream, consisting, for example, of an anti-bacterial membrane.
However, the known devices have even more drawbacks to which the present invention affords a solution. When, in particular, they are used for treating disorders of the eye, the liquid needs to be instilled into the eye of the patient drop by drop, and this operation is all the more tricky as it is commonly performed by the patient himself.
More generally, these devices do not give the desired precision in the correct metering of the product. On the one hand, it is difficult to exert the desired slow and uniform repetitive expulsion pressure and if, for example, when pressing on the outer wall of the flask, one presses too quickly, one does not manage to form drops and too much product is expelled in one shot. Furthermore, the pressure to be exerted by the user varies in the course of the use of the device. It increases as the product is used up, and at the end of the useful life, there is still a dead volume of unusable liquid left inside the flask.
The invention therefore aims to be able to obtain a low and uniform liquid delivery rate as is desirable for the formation of drops, at the same time escaping the influence of the conditions under which the deformable walls of the flask are manipulated so that the dispenser can truly operate as a dropper. It also aims to allow fuller use of the product initially introduced into the flask.
Through its various features, as will be defined and described hereinafter and as may advantageously be applied on an industrial scale, the invention does not only provide control over the formation and ejection of individual drops but also allows the operating security of the packaging device to be improved in terms of its other functions such as the degree of purity of the product, makes it easier to manufacture on an industrial scale and allows cost to be reduced.
In order to achieve its various objectives, the invention proposes a device for packaging a liquid that is to be dispensed drop by drop, comprising a flexible-walled flask that can be deformed manually to gradually decrease its internal volume towards a rigid neck in which is mounted a dispensing head ending in a conduit for expelling the liquid out of the flask, characterized in that this device comprises a microporous pad inserted in the body of the dispensing head across the cross-sectional area for the passage of the liquid between the flask and the expulsion conduit upstream of a liquid-distribution chamber formed between a downstream face of the pad and the expulsion conduit.
This pad has the effect of creating a head loss which regulates the flow of liquid driven through it by the pressure generated in the flask as its volume is reduced. The dose which passes through it each time the user exerts a compressive action on the flask collects in the buffer volume of the distribution chamber before leaving via the expulsion conduit in the form of clearly distinct drops. On this subject, it would seem that the device according to the invention is capable of operating particularly well when the distribution chamber has a large enough volume to accommodate a dose of one to three drops of liquid.
A microporous pad which proves satisfactory according to the invention is advantageously made of a material which is inert with respect to the liquid contained in the flask. Appropriate materials will, in particular, be felts or foams with highly porous open pores such as can be obtained in known ways from various organic polymer resins. In the main applications of the invention, it is advantageous for the microporous pad to be made in the form of a pellet of polyester resin or modified polyester resin felt, such as, in particular, low-density polyethylene resins or polyether sulphone resins.
Resins of this type or the equivalent, which are of course known per se, have the benefit, in the context of the invention, of lending themselves to the production of a cylindrical pad, with diameters from 0.5 to 3 cm and lengths of between 0.2 and 1 cm, with sufficient flexibility that they can be leaktightly force-fitted into the, advantageously cylindrical, body of the dispensing head and can offer, for the passage of the liquid in the longitudinal direction, microducts with a mean pore diameter that can be chosen from between 0.3 and 10 microns.
The above ranges of sizes are particularly suited to affording the desired effect in the case, in particular, of aqueous medicinal solutions, such as solutions for treating the cornea or any other solution intended to be administered to the eye as drops.
In a lock chamber as mentioned hereinabove with regard to the prior art illustrated by the French patent in the name of the applicant published under the Ser. No. 2,638,428, the pad of the device of the invention is configured and arranged in such a way that it occupies the said lock chamber over its entire cross-sectional area and preferably does so over one to two thirds of its longitudinal height, the remainder of this height being reserved for the distribution chamber.
Combining the said pad with a downstream filtration element of an anti-bacterial membrane type is also advantageous, for protecting the liquid contained in the flask and preventing it from becoming contaminated from the ambient air. A particularly well-suited membrane commonly has a thickness of a few tenths of a millimetre and a mean mesh size of between 0.2 and 0.8 microns. When impregnated with solution, it prevents ambient air from entering the flask to replace the liquid expelled. It is therefore clear that, in itself, the pad recommended by the invention is completely different from this both in terms of its structure and in terms of its function.
In combination with the presence of a downstream filtration or purification element advantageously consisting of an anti-bacterial membrane, the invention has as a secondary feature the fact that this element is arranged pressed against a nozzle connected to the body of the dispensing head in which the expulsion conduit is formed. In practice, it should be understood here that the membrane is held flat between two plates which are nevertheless perforated, so as to prevent any liquid remaining between two dispensing steps and damping the membrane, as this would detract from its operation.
By way of a preferred example, a plate of this kind may be made of the material of the dispensing head by fins in a star configuration forming a separator between the downstream face of the microporous pad and the anti-bacterial membrane. In collaboration with these fins, the nozzle will advantageously have grooves set out as concentric annular sectors around a central orifice of the expulsion conduit.
Incidentally, the dispensing head, constituting an insert or pod in the neck of the flask, may additionally bear another purification element located upstream of the microporous pad, particularly an element which is conventional in itself and intended to rid the expelled liquid of a preservative, which is then held back in the flask as desirable, for example, in the case of ophthalmic solutions. In accordance with other embodiments of the device of the invention, the same pad may combine a number of the above functions. This will, in particular, be the case if the pad has a layer of coating or appropriate treatment on its upstream face.
In any event, the regulation afforded by the pad of the device of the invention on the stream of liquid driven through it, preventing exaggerated overpressures from manifesting an effect beyond the flask itself, allows the imposition of the pressure difference between the inside of the flask and the outside to be the one best suited to the formation of drops. However, it would also seem that the distribution of liquid passing uniformly along the microducts across the entire cross-sectional area of its path before collecting in the distribution chamber upon leaving the pad makes a great contribution to the beneficial effect afforded by the invention.
Other features of the invention are directly associated with the foregoing in so far as the improved conditions under which the drops are formed allow the construction of the device as a whole to be better suited to the practical requirements in varied sizes and capacities and allow it to be manufactured more easily at lower cost.
According to one of the embodiments of the device of the invention, the wall of the flask is of cylindrical overall shape in the form of a longitudinally deformable bellows ending in a rigid transverse bottom. It is advantageously made as a single piece of material that can be moulded with the rigid neck for the mounting of the dispensing head and with an outer reinforcing ring protruding radially from the overall size of the bellows so as to allow it to be grasped by an automatic assembly machine without touching the more delicate wall of the said bellows.
Provision is advantageously made for such a bellows-type flask to be mounted via its neck inside a protective outer casing which envelopes it over most of its length. The above outer ring is then extremely useful for carrying out an assembly process which consists in forcibly pushing the flask into this casing by handling it using a tube in abutment against the ring.
When it is desirable for the bellows wall to be compressible over practically all of its length, a very suitable solution consists in giving the casing that protects the bellows a length at least equal to that of the uncompressed bellows while at the same time equipping it with a slot for access from its open bottom.
However, the invention gives preference over this solution to the solution whereby the said casing has a continuous cylindrical periphery and is associated with a closure cover which fits onto it as a continuation thereof, and is removable to give access to the bottom of the flask. This not only has the advantage of affording better protection to the flexible flask, but also has the advantage of being better suited to automated manufacture with the affixing of adhesive labels stuck around the cylindrical casing.